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UntitledADVANCED CONSTRUCTION TECHNOLOGY FOURTH EDITION
ROY CHUDLEY MCIOB
Pearson Education Limited
Visit us on the World Wide Web at:
www.pearsoned.co.uk
© Longman Group Limited 1976, 1977
© Longman Group UK Limited 1987
© Pearson Education Limited 1999, 2006
The rights of Roy Chudley and Roger Greeno to be identified as
authors of this work have
been asserted by them in accordance with the Copyright, Designs and
Patents Act 1988.
All rights reserved; no part of this publication may be reproduced,
stored in any retrieval
system, or transmitted in any form or by any means, electronic,
mechanical, photocopying,
recording, or otherwise without either the prior written permission
of the Publishers or a
licence permitting restricted copying in the United Kingdom issued
by the Copyright
Licensing Agency Ltd, 90 Tottenham Court Road, London W1T
4LP.
First published (as Construction Technology) 1976 (Volume 3), 1977
(Volume 4)
Second edition 1987
Third edition (published as a single volume, with revisions by
Roger Greeno) 1999
Reprinted 1999, 2001, 2002 (twice), 2003, 2004 (twice)
Fourth edition 2006
British Library Cataloguing in Publication Data
A catalogue entry for this title is available from the British
Library
ISBN-10 0-132-01985-X
ISBN-13 978-0-13-201985-9
Set by 35 in 10/12pt Ehrhardt
Printed in Great Britain by Henry Ling Ltd, at the Dorset Press,
Dorchester, Dorset
Preface to third edition vi Preface to fourth edition vii
Acknowledgements viii
INTRODUCTION 1
PART 1 SITE WORKS 3
1.1 Site layout 5 1.2 Electricity on building sites 22 1.3 Lighting
building sites 28 1.4 Winter building 40
PART 2 PLANT AND EQUIPMENT 51
2.1 Builders’ plant: general considerations 53 2.2 Small powered
plant 58 2.3 Earth-moving and excavation plant 70 2.4 Plant for
transportation 86 2.5 Concrete mixers and pumps 114 2.6 Scaffolding
124
PART 3 SUBSTRUCTURE: 1 133
3.1 Groundwater control 135 3.2 Deep trench excavations 148 3.3
Cofferdams and caissons 161 3.4 Tunnelling and culverts 179
CONTENTS
PART 4 SUBSTRUCTURE: 2 191
4.1 Underpinning 193 4.2 Piled foundations 205 4.3 Subsoil analysis
and foundations 231 4.4 Deep basements 248
PART 5 DEMOLITION AND TEMPORARY WORK 259
5.1 Shoring 261 5.2 Demolition 271
PART 6 PORTAL FRAMES 281
6.1 Portal frame theory 283 6.2 Concrete portal frames 287 6.3
Steel portal frames 294 6.4 Timber portal frames 299
PART 7 FIRE 305
7.1 The problem of fire 307 7.2 Structural fire protection 310 7.3
Means of escape in case of fire 341
PART 8 CLADDINGS TO FRAMED STRUCTURES 367
8.1 Cladding panels 369 8.2 Infill panels 375 8.3 Jointing 382 8.4
Mastics, sealants and gaskets 389 8.5 Curtain walling 392 8.6
Rainscreen cladding 402 8.7 Structural glass cladding 409 8.8
Sustainable construction 415
PART 9 FORMWORK SYSTEMS 417
9.1 Wall formwork 419 9.2 Patent formwork 430 9.3 Concrete surface
finishes 439
PART 10 PRESTRESSED CONCRETE 445
10.1 Prestressed concrete: principles and applications 447 10.2
Prestressed concrete systems 462
Contents v
PART 11 BUILDINGS FOR INDUSTRIAL AND STORAGE USE 473
11.1 Factory buildings: roofs 475 11.2 Factory buildings: walls 491
11.3 Wind pressures 497 11.4 Driving rain 503 11.5 Roof structures
507
PART 12 STAIRS 535
PART 13 INTERNAL COMPONENTS AND DECORATIONS 563
13.1 Partitions, doors and ceilings 565 13.2 Painting and
decorations 580
PART 14 EXTERNAL WORKS 583
14.1 Roads, pavings and slabs 585
PART 15 ACCESS AND FACILITIES FOR DISABLED PEOPLE: BUILDINGS OTHER
THAN DWELLINGS 603
15.1 Access to buildings 605 15.2 Access into buildings: entrances
610 15.3 Accessibility within buildings 613 15.4 Use of facilities
619 15.5 Sanitary accommodation 621
Bibliography 624 Index 626
Roy Chudley’s Construction Technology was first published in four
volumes,
between 1973 and 1977. The material has since been continuously
updated through
numerous reprints and full second editions in 1987. The books have
gained a world-
wide readership, and their success – and their impact on
construction education – is
a tribute to Roy Chudley’s experience in further and higher
education and his
talents as a skilled technologist, illustrator and writer.
As a former colleague, it has been a privilege to once again work
with Roy, on
this occasion revising his original work, and compiling the
material into two books:
Construction Technology and Advanced Construction Technology. The
content forms a
thorough study for all students of building, construction
management, architecture,
surveying and the many other related disciplines within the diverse
construction
profession.
The original presentation of comprehensive text matched by
extensive
illustration is retained. Changes in legislation, such as the
Building and
Construction Regulations, have been fully incorporated into the
text; however,
as much of the original work as possible has been purposely
retained as it contains
many relevant examples of existing construction. Additional
material discusses the
new developments and concepts of contemporary practice.
The two new volumes are complementary, as many of the topics
introduced
in Construction Technology are further developed here. Together the
books
provide essential reading for all students aspiring to management,
technologist
and professional qualifications. They should be read alongside the
current local
building regulations and national standards, and where possible
supplemented by
direct experience in the workplace.
Roger Greeno
Guildford 1998
These have included new procedures, relative to legislative and
practice changes.
This revised edition develops these further, with greater attention
to information
and detail. It also incorporates more recent issues, especially
aspects of the Building
Regulations that require buildings to be designed and constructed
to higher energy-
efficient standards. The responsibilities on building designers and
owners with
regard to human rights are considered in a new chapter outlining
the facilities
required for the convenience of the less able using buildings other
than dwellings.
Notwithstanding contemporary requirements, the book’s
established
construction principles are retained. These provide a useful
reference to existing
building stock, and, where appropriate, modifications are included
to illustrate
ongoing change.
The content represents the basic elements of construction practice.
The book
is neither extensive nor prescriptive, as there is insufficient
space in any book to
include every possible means for constructing commercial and
industrial buildings.
However, the content is generally representative, and the reader is
encouraged
to develop their knowledge through experiential learning,
observation in the
workplace, and reading manufacturer’s literature and technical
articles in
professional journals. Reference sources for supplementary reading
are provided
throughout.
In conjunction with this edition’s companion volume, Construction
Technology,
the reader should gain an appreciation of the subject material to
support progression
through any technical, academic or professional qualification study
programme that
includes construction as core or supplementary modules.
Roger Greeno
Guildford 2006
PREFACE TO FOURTH EDITION
This book originated in the 1970s as part of a four-volume series
written by Roy
Chudley. As a result of its popularity, numerous reprints and a new
edition
followed. In 1998 the series was rewritten by Roger Greeno as two
separate
volumes: the initial two volumes formed the basis for the companion
title,
Construction Technology, and the remainder, Advanced Construction
Technology.
The book’s endurance is a tribute to Roy’s initial work in
representing
construction practice with comprehensive illustrative guidance and
supporting text.
I am particularly grateful to the founding author for allowing me
the opportunity
to continue this work and to emulate his unique presentation. I am
also grateful to
the late Colin Bassett as general editor. It was his initiative and
enthusiasm that
encouraged me to pursue this work.
No book can succeed without a good publisher, and Pearson Education
have
fulfilled that role with their supportive editorial and production
team. In particular,
Pauline Gillett has been a constant source of direction and help
throughout the
preparation of the manuscript.
Roger Greeno
Guildford 2006
We are grateful to the Building Research Establishment and The
Stationery Office
Ltd for permission to reproduce material from the BRE Digests and
various Acts,
Regulations and Statutory Instruments.
Extracts from British Standards are reproduced with the permission
of BSI.
Complete copies can be obtained by post from BSI Customer Services,
389
Chiswick High Road, London W4 4AL.
ACKNOWLEDGEMENTS
Advanced Construction Technology is a development of the relatively
elementary
construction detailed in the associated volume, Construction
Technology. This
volume augments the associated volume with further topics relating
to domestic
buildings and lightweight-framed structures, in addition to
concentrating primarily
on complex and specialised forms of construction.
It is designed to supplement a student’s lecture notes, projects
and research
assignments as well as to provide a valuable professional
reference. It also
complements the associated subjects of science, mathematics,
materials technology,
design procedures, structural analysis, structural design,
services, quantity
surveying, facilities management and management studies, and is
therefore
appropriate for most undergraduate and higher-level construction
study
programmes.
The format adopted follows that of Construction Technology,
providing concise
notes and generous illustrations to elaborate on the text content.
The reader should
appreciate that the illustrations are used to emphasise a point of
theory and must
not be accepted as the only solution. A study of working drawings
and details
from building appraisals given in the various construction journals
will add to
background knowledge and comprehension of construction
technology.
No textbook or work of reference is ever complete. Therefore
readers are
recommended to seek out all sources of reference on any particular
topic of study,
to maximise information and to gain a thorough comprehension of the
subject.
Construction technology is not purely academic; lectures and
textbooks can only
provide the necessary theoretical background to the building
processes of design
and site application. Practical experience and monitoring of work
in progress are
essential components of any study programme involving the subject
of construction
technology.
INTRODUCTION
SITE WORKS
PART 1
The construction of a building can be considered as production with
a temporary
factory, the building site being the ‘factory’ in which the
building contractor
will make the product. To enable this activity to take place the
builder requires
operatives, materials and plant, all of which have to be carefully
controlled so
that the operatives have the right machines in the most
advantageous position,
the materials stored so that they are readily available and not
interfering with
the general site circulation, and adequate storage space and site
accommodation.
There is no standard size ratio between the free site space
required to construct
a building and the total size of the site on which the building is
to be erected:
therefore each site must be considered as a separate problem in
terms of allocating
space for operatives, materials and plant. To obtain maximum
efficiency there is
an optimum way of laying out the site and also a correct amount of
expenditure
to support the proposed site layout. Any planned layout should be
reviewed
periodically and adjusted to suit the changing needs of the site
activities. If this
aspect of building construction is carefully considered, planned
and controlled,
it will be reflected in the progress and profitability of the
contract.
Before any initial planning of the site layout can take place
certain preliminary
work must be carried out, preferably at the pre-tender stage. The
decision to tender
will usually be taken by the managing director or, for small works,
by the senior
estimator up to a contract value laid down by the managing
director. With given
designs and specifications the best opportunity for the contractor
to prepare a
competitive and economic tender is in the programming and planning
of the
construction activities. A thorough study of the bill of quantities
will give an
indication of the amount and quality of the materials required and
also of the
various labour resources needed to carry out the contract. A
similar study of the
drawings, together with the bill of quantities and the
specification, will enable the
builder to make a preliminary assessment of the size and complexity
of the contract,
the plant required, and the amount of money that can reasonably be
expended on
1.1
labour-saving items such as concrete mixing and placing
alternatives, handling and
transporting equipment and off-site fabrication of such items as
formwork and
reinforcement.
Before the estimator can make a start on calculating unit rates a
site investigation
should be carried out, preferably by the site manager, who will
supervise the
contract should the tender be successful. The manager’s report
should include
the following information:
n Access to site On- and off-site access, road and rail facilities,
distances
involved, rights of way restrictions, local authority or police
restrictions and
bridge weight or height limitations on approach routes.
n Services Available power and water supplies, together with rates
of payment,
nuisance or value of services already on site, diversions required,
and the time
element involved in carrying out any necessary diversions together
with cost
implications.
n Layout General site conditions such as nature of soil, height of
water table,
flooding risks, tidal waters, neighbouring properties, preservation
orders, trees,
demolition problems and special insurance considerations.
n Staff Travel distances, availability of local trade contractors,
specialist
contractors, local rates of pay and facilities to be provided, e.g.
site
accommodation, catering, health and safety equipment.
n Security Local vandalism and pilfering record, security
contractors’ facilities,
need for night security, fencing and hoarding requirements.
With the knowledge and data gained from contract documents,
site
investigations, and any information gained from the police and
local authority
sources the following pre-tender work can now be carried out:
n Pre-tender programme Usually in a barchart form showing the
proposed
time allowances for the major activities.
n Pre-tender health and safety plan This is prepared by the
project
coordinator (usually the architect) to enable tendering contractors
to consider
the practical and cost implications and adequacy of their resources
with regard
to assessment of risk in safety issues and provision of welfare
requirements.
n Cost implications Several programmes for comparison should be
made to
establish possible break-even points giving an indication of
required bank loan,
possible cash inflow and anticipated profit.
n Plant schedule This can be prepared in the form of a barchart and
method
statements showing requirements and utilisation, which will help in
deciding
how much site maintenance, equipment and space for plant
accommodation
will be needed on site. Consideration of whether to purchase or
hire plant
can be ascertained from these data, although this is only likely to
affect smaller
items such as specialised tools, as few builders could justify
owning large items
of plant. However, a balance of buying and hiring will have to be
established at
this stage.
n Materials schedule Basic data can be obtained from the bill of
quantities.
The buyer’s knowledge of the prevailing market conditions and
future trends
Site layout 7
will enable usage and delivery periods and the amount of site space
and/or
accommodation required to be predicted.
n Labour summary Basic data obtained from the bill of quantities,
site
investigation report and pre-tender barchart programme to establish
number
of subcontract trades required. Also the quantity and type of site
personnel
accommodation required.
n Site organisation structure This is a ‘family tree’ chart showing
the
relationships and interrelationships between the various members of
the
site team, and is normally required only on large sites where the
areas of
responsibility and accountability must be clearly defined.
n Site layout Site space allocation for materials storage, working
areas, units of
accommodation, plant positions and general circulation areas.
Access and egress
for deliveries and emergency services.
n Protection Protection of adjacent buildings, structures
(including trees) with
preservation orders and provision of fencing/hoarding to prevent
trespass and to
protect people in the vicinity. Check adequacy of insurances.
nnn PLANNING SITE LAYOUTS
When planning site layouts the following must be taken into
account:
n site activities;
SITE ACTIVITIES
The time needed for carrying out the principal activities can be
estimated from the
data obtained previously for preparing the material and labour
requirements. With
repetitive activities estimates will be required to determine the
most economical
balance of units that will allow simultaneous construction
processes; this in turn
will help to establish staff numbers, work areas and material
storage requirements.
A similar argument can be presented for overlapping activities. If
a particular
process presents a choice in the way the result can be achieved the
alternatives
must be considered: for example, the rate of placing concrete will
be determined by
the output of the mixer and the speed of transporting the mix to
the appropriate
position. Alternatives that can be considered are:
n more than one mixer;
n regulated supply of ready-mixed concrete;
n on large contracts, pumping the concrete to the placing
position.
All alternative methods for any activity will give different
requirements for staff
numbers, material storage, access facilities and possibly plant
types and numbers.
8 Advanced Construction Technology
EFFICIENCY
To achieve maximum efficiency the site layout must aim at
maintaining the desired
output of the planned activities throughout the working day, and
this will depend
largely upon the following factors:
n Avoidance, as far as practicable, of double handling of
materials.
n Proper storekeeping arrangements to ensure that the materials are
of the correct
type, in the correct quantity, and available when required.
n Walking distances kept to a minimum to reduce the non-productive
time spent
in covering the distances between working, rest and storage areas
without
interrupting the general circulation pattern.
n Avoidance of loss by the elements by providing adequate
protection for unfixed
materials on site, thereby preventing time loss and cost of
replacing damaged
materials.
n Avoidance of loss by theft and vandalism by providing security
arrangements in
keeping with the value of the materials being protected and by
making the task
difficult for the would-be thief or vandal by having adequate
hoardings and
fences. Also to be avoided is the loss of materials due to
pilfering by site staff,
who may consider this to be a perquisite of the industry. Such
losses can be
reduced by having an adequate system of stores’ requisition and
material
checking procedures. Engaging specialist subcontractors on a
‘supply and fit’
basis may reduce the main contractor’s concern.
n Minimising on-site traffic congestion by planning delivery
arrivals, having
adequate parking facilities for site staff cars and mobile
machinery when not in
use, and by having sufficient turning circle room for the types of
delivery vehicle
likely to enter the site.
MOVEMENT
Apart from the circulation problems mentioned above, the biggest
problem is one
of access. Vehicles delivering materials to the site should be able
to do so without
difficulty or delay. Many of the contractors’ vehicles will be
lightweight and will
therefore present few or no problems, but the weight and length of
suppliers’
vehicles should be taken into account. For example, a fully laden
ready-mix
concrete lorry can weigh 20 tonnes, and lorries used for delivering
structural steel
can be 18.000 metres long, weigh up to 40 tonnes and require a
large turning circle.
If it is anticipated that heavy vehicles will be operating on site
it will be necessary
to consider the road surface required. If the roads and paved areas
are part of the
contract and will have adequate strength for the weight of the
anticipated vehicles
it may be advantageous to lay the roads at a very early stage in
the contract, but if
the specification for the roads is for light traffic it would be
advisable to lay only the
base hoggin or hardcore layer at the initial stages because of the
risk of damage to
the completed roads by the heavy vehicles. As an alternative it may
be considered
a better policy to provide only temporary roadways composed of
railway sleepers,
metal tracks or mats until a later stage in the contract,
especially if such roads will
only be required for a short period. See also the Construction
(Health, Safety and
Welfare) Regulations 15 to 17.
Site layout 9
CONTROL
This is concerned mainly with the overall supervision of the
contract, including
staff, materials, and the movement of both around the site. This
control should
form the hub of the activities, which logically develops into areas
or zones of
control radiating from this hub or centre. Which zone is selected
for storage,
accommodation or specific activities is a matter of conjecture and
the conditions
prevailing on a particular site, but as a rule the final layout
will be one of
compromise, with storage and accommodation areas generally
receiving priority.
FACILITIES
These must be planned for each individual site, but certain factors
will be common
to all sites – not least the implications of the Construction
(Health, Safety and
Welfare) Regulations 1996, the Work at Height Regulations 2005 and
the Health
and Safety at Work etc. Act 1974. The main contractor is obliged to
provide a safe,
healthy place of work, and safe systems of work, plant and
equipment that are not a
risk to health. Equipment for the conduct of work must be provided
with adequate
information for its safe use and, where appropriate, training in
its application. Both
regulations are wide ranging and set goals or objectives relating
to risk assessment to
ensure reasonably practicable steps are taken to ensure safety
provision. Prescriptive
requirements for such provisions as scaffold guard rail heights and
platform widths
are scheduled in the Work at Height Regulations.
The principal considerations under the Construction (Health, Safety
and
Welfare) Regulations can be summarised as follows:
n Regulation 5: Safe places of work. This requires that people are
provided with
properly maintained safe surroundings in which to work, along with
safe means
of accessing and leaving that place of work. It is an overall
requirement for
reasonable precautions to be taken, with the perceived and varying
risk associated
with every place of work. Sufficient and suitable working space
should be
provided with regard to the activity being undertaken.
n Regulation 7: Precautions against falling through fragile
material. This applies
mainly to work at heights in excess of 2 m, although potential for
falls from any
height must be assessed. Requirements for sufficient and adequate
means of
guarding persons from fragile material must be in place, with a
prominence of
warning notices displayed in the vicinity (see also Work at Height
Regulations).
n Regulation 8: Falling objects. This requires sufficient and
suitable means for
preventing injury to persons from falling objects. Provisions may
include guard
rails, toe boards and protective sheeting to scaffold systems. No
material to be
tipped or thrown from height (see rubble chutes, Chapter 5.2).
Material to be
stored or stacked in a stable manner to prevent collapse or
unintentional
movement.
n Regulations 9 to 11: Work on structures. A large amount of work
associated with
the construction of buildings is essentially temporary. Therefore
potential for
structural collapse, e.g. inadequately supported formwork, is very
real and must
be recognised and assessed by a competent person. The necessary
precautions
must be taken to prevent danger. Demolition and dismantling are
also high-risk
10 Advanced Construction Technology
areas, justifying thorough planning and risk analysis before and as
work
proceeds.
n Regulations 12 and 13: Excavation, cofferdams and caissons.
Substructural work
has an inherent danger of collapse. Suitable provision to prevent
collapse of
trenches etc. must be designed and installed by competent
specialists. Awareness
of water-table levels and possible variations, e.g. seasonal and
tidal, is essential,
as is location of underground cables and other services that could
be a danger.
n Regulation 14: Prevention of drowning. This is not applicable to
all sites,
but if there is a danger from water or other liquids in any
quantity then every
practical means possible must be taken to prevent people falling
into it. Personal
protective and rescue equipment must be available, maintained in
good order,
and water transport must be provided under the control of a
competent person.
n Regulations 15 to 17: Traffic routes, vehicles, doors and gates.
These make
provision for segregation of vehicles and pedestrians, with
definition of routes.
The regulations require adequate construction and maintenance of
temporary
traffic routes, control of unintended traffic movement, warnings
(audible or
otherwise) of vehicle movements, prohibition of misuse of vehicles,
and
safeguards for people using powered doors and guards such as that
on
hoist facilities.
n Regulations 18 to 21: Prevention and control of emergencies.
These make
provision for emergency routes, means of escape, evacuation
procedures,
adequate signing, firefighting equipment, emergency lighting and
associated
training for dealing with emergencies.
n Regulation 22: Welfare facilities. Minimum requirements apply
even to the
smallest of sites. These include an adequate supply of drinking
water, sanitary
and washing facilities, means to heat food and boil water, adequate
outdoor
protection including personal protective equipment (PPE), rest
accommodation
and facilities to eat meals, first-aid equipment under the control
of an appointed
person, and accommodation to change and store clothing.
n Regulations 23 to 27: Site-wide issues. General requirements to
ensure fresh air
availability at each workplace, reasonable temperatures maintained
at internal
workplaces, protection against inclement weather, adequate levels
of lighting
(including emergency lights), reasonably clean and tidy workplaces,
well-defined
site boundaries, and maintenance of site equipment and plant for
safe use by
operatives.
n Regulations 28 to 30: Training, inspection and reports.
Specialised elements
of work to be undertaken only by those appropriately qualified
and/or trained.
Supervision of others by those suitably qualified may be
acceptable. Places of
obvious danger and risk, such as excavations, cofferdams and
caissons, to be
inspected regularly (at least daily and when changes are effected)
by a competent
person. Written records/reports to be filed after every
inspection.
The principal considerations under the Work at Height Regulations
apply to any
place at or below ground level as well as above ground. They also
include the means
of gaining access and egress from that place of work. Measures
taken by these
regulations are designed to protect a person from injury caused by
falling any
Site layout 11
distance. This may be from plant and machinery or from equipment
such as
scaffolding, trestles and working platforms, mobile or static. In
summary:
n Regulation 4: Organisation and planning. It is the employer’s
responsibility
to ensure that work at height is planned, supervised and conducted
in a safe
manner. This includes provisions for emergencies and rescues, and
regard for
assessing risk to persons working during inclement weather.
n Regulation 5: Competence. Employer’s responsibility to ensure
that persons
engaged in any activity relating to work at height are competent.
Any person
being trained to be supervised by a competent person.
n Regulation 6: Risk avoidance. Re risk assessment under Regulation
3 of the
Management of Health and Safety at Work Regulations. This is
concerned
primarily with appraisal of the work task relative to its
situation: that is, work
should not be undertaken at a height if it is safer to do it at a
lower level, e.g.
cutting materials. Provisions to be in place for preventing persons
sustaining
injury from falling.
n Regulation 7: Work at height equipment. Further requirements for
assessment of
risk relative to the selection of plant and equipment suitable for
collective rather
than individual use.
Scaffold and working platforms:
n Top guard rail, min. 950 mm high.
n Intermediate guard rail, positioned so that no gap between it and
top rail or
toe board exceeds 470 mm.
n Toe board, sufficient to prevent persons or materials falling
from the working
platform. Generally taken as 150 mm min. height. For practical
purposes a
225 mm wide scaffold board secured vertically.
n Stable and sufficiently rigid for the intended purpose.
n Dimensions adequate for a person to pass along the working
platform,
unimpeded by plant or materials.
n No gaps in the working platform.
n Platform surface resistant to slipping or tripping.
n Platform designed to resist anticipated loading from personnel,
plant and
materials.
n Scaffold frame of sufficient strength and stability.
n If the scaffold is unconventional in any way, calculations are
required to prove
its structural integrity.
n Assembly, use and dismantling plan and instructions to be
produced by a
competent designer. A standard procedure/plan is acceptable for
regular
applications.
n During assembly, alteration, dismantling or non-use, suitable
warning signs
to be displayed as determined by the Health and Safety (Safety
Signs and
Signals) Regulations. Means to prevent physical access also
required.
n Assembly, alteration and dismantling under the supervision of a
competent
person qualified by an approved training scheme.
Nets, airbags or other safeguards for arresting falls:
12 Advanced Construction Technology
Used where it is considered not reasonably practical to use other
safer work
equipment without it. A safeguard and its means for anchoring must
be of
adequate strength to arrest and contain persons without injury,
where they are
liable to fall. Persons suitably trained in the use of this
equipment, including
rescue procedures, must be available throughout its deployment.
Where personal
fall protection equipment is considered necessary, it should be
correctly fitted to
the user, adequately anchored, and designed to prevent unplanned
use by the
user’s normal movements.
Ladders:
n Used solely where a risk assessment indicates that it is
inappropriate and
unnecessary to install more substantial equipment. Generally, this
applies to
work of a short duration.
n The upper place of support is to be firm, stable and strong
enough to retain
the ladder without movement. Position to be secured by rope lashing
or other
mechanical fixing.
n Inclination is recommended at approximately 75° to the vertical,
i.e. in the
vertical to horizontal ratio of 4:1.
n A suspended ladder to be secured and attached to prevent
displacement and
swinging.
n The extension of a ladder beyond a place of landing should be
sufficient for
safe bodily transfer – normally taken as 1.050 m min. measured
vertically.
n Where a ladder ascends 9.000 m or more vertically, landing points
to be
provided as rest platforms.
n Regulation 9: Fragile surfaces. It is the employer’s
responsibility to ensure that
no person works on or near a fragile surface. Where it is
impossible to avoid,
then sufficient protection, e.g. platforms, guard rails etc., are
to be provided.
Location of fragile surfaces is to be indicated by positioning of
prominent
warning signs.
n Regulation 10: Falling objects. See also Regulation 8 under the
Construction
(Health, Safety and Welfare) Regulations. Suitable provisions, e.g.
fan hoardings,
are required to prevent persons suffering injury from falling
objects or materials.
Facilities are to be provided for safe collection and transfer of
materials between
high and low levels, e.g. chutes. No objects to be thrown.
Materials to be stacked
with regard to their stability and potential for movement.
n Regulation 11: Dangerous areas. Areas of work of specific danger,
e.g.
demolition, to be isolated to ensure that persons not engaged in
that particular
activity are excluded. Warning signs to be displayed.
n Regulations 12 and 13: Inspection. These regulations specifically
apply to
scaffolding, ladders and fall protection equipment. After
installation or assembly,
no equipment may be used until it has been inspected and documented
as safe to
use by a competent person. Further inspections are required where
conditions
may have caused deterioration of equipment, or alterations or
changes have been
made. Following an interval, every place of work at height should
be inspected
before work recommences.
n Regulation 14: Personnel duties. Persons working at height should
notify their
supervisor of any equipment defect. If required to use personal
safety/protective
Site layout 13
equipment (PPE), individuals should be adequately trained and
instructed in
its use.
Under the Health and Safety at Work etc. Act employers must have
defined duties,
which include providing:
n safe access to and egress from places of work;
n safe systems of work;
n safe items of plant and equipment;
n suitable and adequate training, supervision and instruction in
the use of
equipment;
n suitable and appropriate PPE applicable to head, hands, feet,
eyes and mouth;
n materials and substances that are safe to use (COSHH Regulations
1999);
n a statement of health and safety policy.
Employees and the self-employed have duties to ensure that they do
not endanger
others while at work. This includes members of the public and other
operatives on
site. They must cooperate with the health and safety objectives of
their employer
(the main contractor), not interfere with any plant or equipment
provided for their
use, other than its intended use, and report any defects to
equipment and dangers
relating to unsafe conditions of work.
The preceding section on provision of facilities under the
Construction Regulations,
the Work at Height Regulations and the Health and Safety at
Work etc. Act is intended as summary comment for guidance only. For
a full
appreciation, the reader is advised to consult each specific
document. These are
published by The Stationery Office, www.tso.co.uk.
ACCOMMODATION
Apart from legislative necessities, the main areas of concern will
be sizing,
equipping and siting the various units of accommodation.
Mess huts
These are for the purposes of preparing, heating and consuming
food, which may
require the following services: drainage, light, power, hot and
cold water supply.
To provide a reasonable degree of comfort a floor area of 2.0 to
2.5 m2 per person
should be allowed. This will provide sufficient circulation space,
room for tables
and seating, and space for the storage of any utensils.
Consideration can also be
given to introducing a system of staggered meal breaks, thus
reducing space
requirements. On large sites where full canteen facilities are
being provided this
will be subcontracted to a catering firm. Mess huts should be sited
so that they do
not interfere with the development of the site but are positioned
so that travel time
is kept to a minimum. On sites that by their very nature are large,
it is worthwhile
considering a system whereby tea breaks can be taken in the
vicinity of the work
areas. Siting mess huts next to the main site circulation and
access roads is not of
14 Advanced Construction Technology
major importance. It is the principal contractor’s responsibility
to ensure that
reasonable welfare facilities are available on site, although they
do not necessarily
have to provide these. It may be part of subcontractors’ conditions
of engagement
that they provide their own.
Drying rooms
Used for the purposes of depositing and drying wet clothes. Drying
rooms generally
require a lighting and power supply, and lockers or racks for
deposited clothes. A
floor area of 0.6 m2 per person should provide sufficient space for
equipment and
circulation. Drying rooms should be sited near or adjacent to the
mess room.
Toilets
Contractors are required to provide at least adequate washing and
sanitary facilities
as set out in Regulation 22 of the Construction (Health, Safety and
Welfare)
Regulations. All these facilities will require light, water and
drainage services.
If it is not possible or practicable to make a permanent or
temporary connection
to a drainage system, the use of chemical methods of disposal
should be considered.
Sizing of toilet units is governed by the facilities being
provided, and if female staff
are employed on site separate toilet facilities must be provided.
Toilets should be
located in a position that is convenient to both offices and mess
rooms, which may
mean providing more than one location on large sites.
First-aid rooms
Only required on large sites as a specific facility, otherwise a
reasonably equipped
mess room will suffice. The first-aid room should be sited in a
position that is
conveniently accessible from the working areas, and must be of such
a size as to
allow for the necessary equipment and adequate circulation, which
would indicate
a minimum floor area of 6 m2. First-aid equipment must be under the
charge of a
suitably trained, appointed person, with responsibility for
accounting for the
contents and their use.
Before the proposed site layout is planned and drawn, the contracts
manager and
the proposed site agent should visit the site to familiarise
themselves with the
prevailing conditions. During this visit the position and condition
of any existing
roads should be noted, and the siting of any temporary roads
considered necessary
should be planned. Information regarding the soil conditions,
height of water table,
and local weather patterns should be obtained by observation, site
investigation, soil
investigation, local knowledge or from the local authority. The
amount of money
that can be expended on this exercise will depend upon the size of
the proposed
contract and possibly upon how competitive the tenders are likely
to be for the
contract under consideration.
Figure 1.1.1 shows a typical small-scale general arrangement
drawing, and needs
to be read in conjunction with Fig. 1.1.2, which shows the proposed
site layout.
Site layout 15
ech n ology
Figure 1.1.2 Site layout example: proposed layout of accommodation
and storage
Site layout 17
The following data have been collected from a study of the contract
documents and
by carrying out a site investigation:
n Site is in a typical urban district within easy reach of the
contractor’s head office
and therefore will present no transport or staffing problems.
n Subsoil is a firm sandy clay with a water table at a depth that
should give no
constructional problems.
n Possession of site is to be at the end of April, and the contract
period is
18 months. The work can be programmed to enable the foundation
and
substructure work to be completed before adverse winter weather
conditions
prevail.
n Development consists of a single five-storey office block with an
in-situ
reinforced concrete structural frame, in-situ reinforced concrete
floors and
roof, precast concrete stairs, and infill brick panels to the
structural frame with
large hardwood timber frames fixed into openings formed by the
bricklayers.
Reduced-level dig is not excessive, but the topsoil is to be
retained for
landscaping upon completion of the building contract by a separate
contractor;
the paved area in front of the office block, however, forms part of
the main
contract. The existing oak trees in the north-east corner of the
site are to be
retained and are to be protected during the contract period.
n Estimated maximum number of staff on site at any one time is 40,
in the ratio of
1 supervisory staff to 10 operatives plus a resident clerk of
works.
n Main site requirements are as follows:
1 office for 3 supervisory staff.
1 office for resident clerk of works.
1 office for reception and materials checker/assistant site
agent.
1 hutment as lock-up store.
1 mess room for 36 operatives.
1 drying room for 36 operatives.
Toilets.
Timber store and formwork fabrication area.
Reinforcement store and fabrication area.
Scaffold store.
Car parking areas.
1 tower crane and area for concrete deliveries, sand and cement
storage, and
site mixer.
Sizing and location of main site requirements can be considered in
the following
manner:
n Offices for contractor’s supervisory staff Area required = 3 ×
3.7 m2 =
11.1 m2. Using plastic-coated galvanised steel prefabricated cabins
based on
a 2.400 m wide module gives a length requirement of 11.1 ÷ 2.4 =
4.625 m:
therefore use a hutment 2.400 m wide × 4.800 m long, giving an area
of 11.52 m2.
Other standard internal widths are 2.7 and 3.0 m, and standard
internal lengths
range from 2.4 to 10.8 m in 1.2 m increments.
18 Advanced Construction Technology
n Office for resident clerk of works Allowing for one visitor
area
required = 2 × 3.7 m2 = 7.4 m2. Using same width module as for
contractor’s
office length required = 7.4 ÷ 2.4 = 3.08 m, therefore using a
2.400 m wide ×
3.600 m long cabin will give an area of 8.64 m2. The contractor’s
office and that
for the clerk of works need to be sited in a position that is
easily and quickly
found by visitors to the site and yet at the same time will give a
good view of
the site operations. Two positions on the site in question seem to
meet these
requirements: one is immediately to the south of the paved area and
the other
is immediately to the west of it. The second position has been
chosen for both
offices because there is also room to accommodate visitors’ cars in
front of the
offices without disturbing the circulation space given by the paved
area.
n Office for reception and materials checker A hut based on
the
requirements set out above for the clerk of works would be
satisfactory. The
office needs to be positioned near to the site entrance so that
materials being
delivered can be checked, directed to the correct unloading point,
and – most
important – checked before leaving to see that the delivery has
been completed.
It also needs to be easily accessible for site visitors, thus
preventing unsupervised
wandering onto the site.
n Lock-up store This needs to be fitted with racks and storage bins
to
house valuable items, and a small unit of plan size 2.400 m × 2.400
m has been
allocated. Consideration must be given to security, and in this
context it has been
decided to combine the lock-up store and the site
manager’s/materials checker’s
office, giving a total floor plan of 2.400 m × 6.000 m. This will
enable the issue
of stores only against an authorised and signed requisition to be
carefully
controlled, the assistant site agent fulfilling the function of
storekeeper.
n Mess room Area required = 36 × 2.5 m2 = 90 m2, using a width
module of
3.000 m, length required = 90 ÷ 3 = 30 m: therefore a number of
combinations
based on the standard lengths listed are possible. Perhaps 3
modules of
10.8 m = 32.4 m total length (97.2 m2) or 5 modules of 6 m length =
30 m
total length (90 m2), the choice depending to some extent on the
disposition of
the site staff, number and size of subcontractors involved. The
mess room needs
to be sited in a fairly central position to all the areas of
activity, and the east end
of the paved area has been selected.
n Drying room Area required = 36 × 0.6 m2 = 21.6 m2, using a width
module
of 3.000 m, length required = 21.6 ÷ 3 = 7.2 m: therefore select a
single length or
2 modules of 3.600 m. The drying room needs to be in close
proximity to the
mess room and has therefore been placed at the east end of the mess
room.
Consideration could be given to combining the mess room and drying
room
into one unit.
n Toilets On this site it is assumed that connection can be made to
existing
drains. If this is not convenient, temporary (or preferably
permanent) drain
branches can be connected to a main sewer. Two such units are
considered to
be adequate, one to be sited near to the mess room and the other to
be sited
near to the office complex. Adequate sanitary conveniences are
required in the
Construction (Health, Safety and Welfare) Regulations 1996. For the
mess toilet
unit catering for 36 operatives two conveniences are considered
minimum, but a
Site layout 19
three-convenience toilet unit will be used, having a plan size of
2.400 m × 3.600 m.
Similarly, although only one convenience is required for the office
toilet unit, a
two-convenience unit will be used with a plan size of 2.400 m ×
2.400 m.
n Materials storage compound An area to be defined by a temporary
plywood
hoarding 2.400 m high and sited at the east end of the paved area
giving good
access for deliveries and within reach of the crane. Plan size to
be allocated
12.000 m wide × 30.000 m long.
n Timber storage Timber is to be stored in top-covered but
open-sided racks
made from framed standard scaffold tubulars. Maximum length of
timber to be
ordered is unlikely to exceed 6.000 m in length: therefore,
allowing for removal,
cutting and fabricating into formwork units, a total plan size of
6.000 m wide ×
36.000 m long has been allocated. This area has been sited to the
south of the
paved area, giving good access for delivery and within the reach of
the crane.
n Reinforcement storage The bars are to be delivered cut to length,
bent
and labelled, and will be stored in racks as described above for
timber storage.
Maximum bar length to be ordered assumed not to exceed 12.000 m:
therefore
a storage and fabrication plan size of 6.000 m wide × 30.000 m long
has been
allocated. This area has been sited to the north of the storage
compound, giving
reasonable delivery access and within reach of the crane.
n Scaffold storage Tube lengths to be stored in racks as described
for timber
storage, with bins provided for the various types of coupler.
Assuming a
maximum tube length of 6.000 m, a plan size of 3.000 m wide ×
12.000 m long.
This storage area has been positioned alongside the west face of
the proposed
structure, giving reasonable delivery access and within reach of
the crane if
needed. The scaffold to be erected will be of an independent type
around the
entire perimeter positioned 200 mm clear of the building face and
of five-board
width, giving a total minimum width of 200 + (5 × 225) = 1.325, say
1.400 m
total width.
n Tower crane To be sited on the paved area in front of the
proposed building
alongside the mixer and aggregate storage position. A crane with a
jib length of
27.000 m, having a lifting capacity of 1.25 tonnes at its extreme
position, has
been chosen so that the crane’s maximum radius will cover all the
storage areas,
thus making maximum utilisation of the crane possible.
n Car parking Assume 20 car parking spaces are required for
operatives,
needing a space per car of 2.300 m wide × 5.500 m long, giving a
total length of
2.3 × 20 = 46.000 m and, allowing 6.000 m clearance for
manoeuvring, a width of
5.5 + 6.0 = 11.500 m will be required. This area can be provided to
the south of
the mess room and drying room complex. Staff car-parking space can
be sited in
front of the office hutments, giving space for the parking of seven
cars, which
will require a total width of 7 × 2.3 = 16.100 m.
n Fencing The north and south sides of the site both face onto
public footpaths
and highways. Therefore a close-boarded or sheet hoarding in
accordance with
the licence issued by the local authority will be provided. A
lockable double gate
is to be included in the south-side hoarding to give access to the
site. The east
side of the site faces an undeveloped site, and the contract calls
for a 2.000 m
high concrete post and chain-link fence to this boundary. This
fence will be
20 Advanced Construction Technology
erected at an early stage in the contract to act as a security
fence during the
construction period as well as providing the permanent fencing. The
west side
of the site has a 2.000 m high brick wall, which is in a good
structural condition,
and therefore no action is needed on this boundary.
n Services It has been decided that permanent connections to the
foul drains
will be made for convenient site use, thus necessitating early
planning of the
drain-laying activities. The permanent water supply to the proposed
office block
is to be laid at an early stage, and this run is to be tapped to
provide the supplies
required to the mixer position and the office complex. A temporary
connection
is to be made to supply the water service to the mess room complex,
because
a temporary supply from the permanent service would mean running
the
temporary supply for an unacceptable distance. An electrical supply
is to be
taken onto site, with a supply incoming unit housed in the
reception office along
with the main distribution unit. The subject of electrical supplies
to building
sites is dealt with in Chapter 1.2. Telephones will be required to
the contractor’s
and clerk of works’ offices. It has been decided that a gas supply
is not required.
n Site identification A V-shaped board bearing the contractor’s
name and
company symbol is to be erected in the south-west corner of the
site in such a
manner that it can be clearly seen above the hoarding by traffic
travelling in both
directions, enabling the site to be clearly identified. The board
will also advertise
the company’s name and possibly provide some revenue by including
on it the
names of participating subcontractors. As a further public
relations exercise it
might be worthwhile considering the possibility of including public
viewing
panels in the hoarding on the north and south sides of the
site.
n Health and safety Attached to the hoarding at the site entrance
is a board
displaying the employer’s policy for corporate site safety. Some
examples of the
standard images that could be used are shown in Fig. 1.1.3.
Figure 1.1.3 Site safety board
Site layout 21
Note: Sign colours Geometric shape Indication
Red on white background, black image Circular with a diagonal line
Prohibition
Yellow with black border, black image Triangular Warning
Blue with white image Circular Mandatory
Green with white image Oblong or square Safe condition
References:
Health and Safety (Safety Signs and Signals) Regulations.
Management of Health and Safety at Work Regulations.
European Directive 92/58 EEC.
The extent to which the above exercise in planning a site layout
would be carried
out in practice will depend upon various factors, such as the time
and money that
can reasonably be expended and the benefits that could accrue in
terms of maximum
efficiency compared with the amount of the capital outlay. The need
for careful
site layout and site organisation planning becomes more relevant as
the size and
complexity of the operation increase. This is particularly true for
contracts where
spare site space is very limited.
A supply of electricity is usually required on construction sites
to provide lighting
to the various units of accommodation. It may also be needed to
provide the power
to drive small and large items of plant. Two sources of electrical
supply to the site
are possible:
n portable self-powered generators;
n metered supply from the local section of the national grid
distribution
network.
As a supply of electricity will be required in the final structure
the second source
is usually adopted, because it is generally possible to connect a
permanent supply
cable to the proposed development for construction operations, thus
saving the cost
of laying a temporary supply cable to the site.
To obtain a metered temporary supply of electricity a contract must
be signed
between the main contractor and a local area electricity marketing
company. They
will require the following information:
n Address of site.
n Site location plan.
n Maximum anticipated load demand in kW for the construction
period. A
reasonable method of estimating this demand is to allow for a
loading of
10 W/m2 for the total floor area of the finished structure and to
add for any
high-load equipment such as cranes, pumps and drying-out heaters
that are
to be used.
n Final load demand of the completed building to ensure that the
correct rating of
cable is laid for the permanent supply.
n Date on which temporary supply will be required.
n Name, address and telephone number of the building owner or their
agent, and
of the main contractor.
Electricity on building sites 23
To ensure that the supply and installation are available when
required by the
builder it is essential that an application for a temporary supply
of electricity is
made at the earliest possible date.
On any construction site it is possible that there may be existing
electricity
cables, which can be advantageous or may constitute a hazard or
nuisance.
Overhead cables will be visible, whereas the routes and depths of
underground
cables can be ascertained only from the records and maps kept by
local area supply
companies. Overhead cable voltages should be checked with the local
area suppliers,
because these cables are usually uninsulated and are therefore
classed as a hazard
due mainly to their ability to arc over a distance of several
metres. High-voltage
cables of over 11 kV rating will need special care, and any of the
following actions
could be taken to reduce or eliminate the danger:
n Apply to the local area supplier to have the cables re-routed at
a safe distance
or height.
n Apply to have the cable taken out of service.
n Erect warning barriers to keep site operatives and machines at a
safe distance.
These barriers must be clearly identified as to their intention,
and they may
be required to indicate the safe distance in both the horizontal
and vertical
directions. The local area supplier will advise on suitable safe
distances according
to the type of cable and the load it is transmitting.
The position and depth of underground cables given by electricity
suppliers must
be treated as being only approximate, because historical records
show only the data
regarding the condition as laid, and since then changes in site
levels may have taken
place. When excavating in the locality of an underground cable
extreme caution
must be taken, which may even involve careful hand excavation to
expose the cable.
Exposed cables should be adequately supported, and suitable
barriers with warning
notices should be erected. Any damage, however minor, must be
reported to the
electricity supplier for the necessary remedial action. It is worth
noting that if a
contractor damages an underground electric cable that was known to
be present,
and possibly caused a loss of supply to surrounding properties, the
contractor can
be liable for negligence, trespass to goods and damages.
nnn SUPPLY AND INSTALLATION
In Great Britain electrical installations on construction sites are
subject to the
requirements of the Electricity Supply Regulations 1988 and the
Electricity at
Work Regulations 1989. These impose duties and expectations on
employers,
employees and the self-employed, for health and safety
responsibilities with regard
to the use of electricity. Risk assessment and suitable precautions
relating to
particular hazards, such as overhead lines and underground cables
encountered
on site, are contained by the Health and Safety at Work etc. Act
1974 and the
Construction (Health, Safety and Welfare) Regulations 1996.
Installations should
follow rules given in BS 7671: Requirements for electrical
installations (Institution
of Electrical Engineers Wiring Regulations). Section 604 details
provision for
temporary installations and installations on construction sites.
See also, BS 7375:
24 Advanced Construction Technology
Code of practice for distribution of electricity on construction
and building sites. The
supply distribution assemblies used in the installation should
comply with the
recommendations of BS 4363: Specification for distribution
assemblies for reduced
low voltage electricity supplies for construction and building
sites. This covers the
equipment suitable for the control and distribution of electricity
from a three-phase
four-wire a.c. system up to a voltage of 400 V with a maximum
capacity of 300
A per phase. BS EN 60309-2 specifies plugs, socket outlets and
cable couplers for
the varying voltages recommended for use on construction
sites.
The appliances and wiring used in temporary installations on
construction sites
may be subject to extreme abuse and adverse conditions: therefore
correct circuit
protection, earthing and frequent inspection are most important,
and this work,
including the initial installation, should be entrusted to a
qualified electrician or
to a specialist electrical contractor.
Electrical distribution cables contain three line wires and one
neutral, which
can give either a 400 V three-phase supply or a 230 V single-phase
supply. Records
of accidents involving electricity show that the highest risk is
encountered when
electrical power is used in wet or damp conditions, which are often
present on
construction sites. It is therefore generally recommended that
wherever possible
the distribution voltage on building sites should be 110 V. This is
a compromise
between safety and efficiency, but it cannot be overstressed that a
supply of this
voltage can still be dangerous and lethal.
The recommended voltages for use on construction sites are given
below:
Mains voltage
400 V three-phase:
n supply to transformer unit, heavy plant such as cranes and
movable plant fed via
a trailing cable;
n hoists and plant powered by electric motors in excess of a 3.75
kW rating.
230 V single-phase:
n installations in site accommodation buildings;
n fixed floodlighting;
n small mobile plant up to 3.75 kW.
110 V single-phase:
n site floodlighting other than fixed floodlighting;
Electricity on building sites 25
n portable hand-lamps;
n local lighting up to 2 kW.
50 V single-phase and 25 V single-phase:
n as listed for 110 V single-phase but being used in confined and
damp situations.
It is worth considering the use of 50 or 25 V battery-supplied
hand-lamps if
damp situations are present on site. All supply cables must be
earthed, and in
particular 110 V supplies should be centre-point earthed so that
the nominal voltage
to earth is not more than 65 V on a three-phase circuit and not
more than 55 V on a
single-phase circuit.
Protection to a circuit can be given by using bridge fuses,
cartridge fuses and
circuit breakers. Adequate protection should be given to all main
and sub circuits
against any short-circuit current, overload current and earth
faults.
Protection through earthing may be attained in two distinct
ways:
n Provision of a path of low impedence to ensure over-current
device will operate
in a short space of time.
n Insertion in the supply of a circuit-breaker with an operating
coil that trips the
breaker when the current due to earth leakage exceeds a
predetermined value.
BS 4363 and BS EN 60309-2 recommend that plug and socket outlets
are
identified by a colour coding as an additional safety precaution to
prevent incorrect
connections being made. The recommended colours are:
25 V – violet
50 V – white
110 V – yellow
230 V – blue
400 V – red
500/650 V – black
The equipment that can be used to distribute an electrical supply
around a
construction site is as follows:
n Incoming site assembly (ISA) Supply, control and distribution of
mains
supply on site – accommodates supply company’s equipment and has
one
outgoing circuit.
n Main distribution assembly (MDA) Control and distribution of
mains
supply for circuits of 400 V three-phase and 230 V
single-phase.
n Incoming site distribution assembly (ISDA) A combined ISA and
MDA
for use on sites where it is possible to locate these units
together.
n Transformer assembly Transforms and distributes electricity at a
reduced
voltage: can be for single-phase, three-phase or both phases and is
abbreviated
TA/1, TA/3 or TA/1/3 accordingly.
n Socket outlet assembly (SOA) Connection, protection and
distribution of
final subcircuits at a voltage lower than the incoming
supply.
n Extension outlet assembly (EOA) Similar to outlet assembly except
that
outlets are not protected.
26 Advanced Construction Technology
Electricity on building sites 27
n Earth monitor unit (EMU) Flexible cables supplying power at mains
voltage
from the MDA to movable plant incorporate a separate pilot
conductor in
addition to the main earth continuity conductor. A very-low-voltage
current
passes along these conductors between the portable plant and the
fixed EMU.
A failure of the earth continuity conductor will interrupt the
current flow, which
will be detected by the EMU, and this device will automatically
isolate the main
circuit.
The cubicles or units must be of robust construction, strong,
durable, rain resistant
and rigid to resist any damage that could be caused by
transportation, site handling
or impact shocks likely to be encountered on a construction site.
All access doors or
panels must have adequate weather seals. Figure 1.2.1 shows a
typical supply and
distribution system for a construction site.
The routeing of the supply and distribution cables around the
construction site
should be carefully planned. Cables should not be allowed to trail
along the ground
unless suitably encased in a tube or conduit, and even this method
should be used
only for short periods of time. Overhead cables should be supported
by hangers
attached to a straining wire and suitably marked with ‘flags’ or
similar visual
warning. Recommended minimum height clearances for overhead cables
are:
n 5.200 m in positions inaccessible to vehicles;
n 5.800 m where cable crosses an access road or any part of the
site accessible to
vehicles.
Cables that are likely to be in position for a long time, such as
the supply to a crane,
should preferably be sited underground at a minimum depth of 500 mm
and
protected by tiles, or alternatively housed in clayware or similar
pipes.
In the interest of safety, and to enable first-aid treatment to be
given in cases of
accident, all contractors using a supply of electricity on a
construction site for any
purpose must display, in a prominent position, extracts from the
Electricity at Work
Regulations. Pictographic safety signs for caution of the risk of
electric shock are
applicable under the Health and Safety (Safety Signs and Signals)
Regulations 1996.
Suitable placards giving instructions for emergency first-aid
treatment for persons
suffering from electrical shock and/or burns are obtainable from
RoSPA, the
St John Ambulance Association, and stockists of custom-made
signs.
Inadequate light accounts for more than 50% of the loss of
production on UK
construction sites between the months of November and February.
Inadequate
lighting also increases the risks of accidents and lowers the
security of the site.
The initial costs of installing a system of artificial lighting for
both internal and
external activities can usually be offset by higher output,
better-quality work, a
more secure site, and apportioning the costs over a number of
contracts on a use
and reuse basis.
The reasons for installing a system of artificial lighting on a
construction site are
as follows:
n Inclement weather, particularly in winter, when a reduction of
natural daylight is
such that the carrying out of work becomes impracticable.
n Without adequate light, all activities on construction sites
carry an increased risk
of accident and injury.
n By enabling work to proceed, losses in productivity can be
reduced.
n Reduces the wastage of labour and materials that often results
from working in
poor light.
n Avoids short-time working due to the inability to see clearly
enough for accurate
and safe working.
n Improves the general security of the site.
The following benefits may be obtained by installing and using a
system of
artificial lighting on a construction site:
n Site activities will be independent of the availability of
natural daylight, and
therefore the activities can be arranged to suit the needs of the
contract, the
availability of materials, and the personnel involved.
n Overtime and extra shifts can be worked to overcome delays that
might occur
from any cause.
Lighting building sites 29
n Deliveries and collection of materials or plant can be made
outside normal site
working hours, thus helping to avoid delays and/or
congestion.
n The amount of spoilt material and the consequent rectification
caused by
working under inadequate light can be reduced.
n It provides an effective deterrent to the would-be trespasser or
pilferer.
n Contractual relationships will be improved by ensuring regular
working hours
and thus regular earnings.
Planning the lighting requirements depends on site layout, size of
site, shape
of site, geographical location, availability of an electrical
supply and the planned
activities for the winter period. Figure 1.3.1 shows two charts
covering various
regions in the UK, giving an indication of the periods when
external and internal
artificial lighting may be required on a construction site under
normal conditions.
Any form of temporary artificial site lighting should be easy to
install and modify
as needs change, and should be easy to remove while works are still
in progress.
The supply and distribution of an electrical service to a
construction site has
already been covered in the previous chapter, and it is therefore
necessary only to
stress again the need for a safe, reliable installation, designed
and installed by a
specialist contractor.
nnn ILLUMINATION
Illumination can be considered as the measure of light or
illuminance falling on
a surface. It is expressed in lux, which is one lumen of light
falling on 1 m2 of
surface, and this can be measured with a small portable lightmeter,
which consists
of a light-sensitive cell generating a small current proportional
to the light falling
on it. The level of illuminance at which an operative can work in
safety and carry
out tasks to an acceptable standard, in terms of both speed and
quality, is quite low,
because the human eye is very adaptable and efficient. Although the
amount of
illuminance required to enable a particular activity to be carried
out is a subjective
measure, depending largely upon the task, and the age and state of
health of the
Table 1.3.1 Typical service values of illuminance
Activities Illuminance (lux)
Painting and decorating 500
Fine craft work 1,000
Lighting building sites 31
operative concerned, Table 1.3.1 presents typical service values of
illuminance.
The values shown in the table do not allow for deterioration, dirt,
bad conditions or
shadow effects. Therefore in calculating the illuminance required
for any particular
situation a target value of twice the service value should be
used.
When deciding on the type of installation to be used, two factors
need to be
considered:
n nature and type of area under consideration.
The properties of the various types of lamp available should be
examined to
establish the most appropriate for any particular site
requirement.
nnn LAMPS
n Tungsten filament lamp Ideal for short periods, such as a total
of 200 hours
during the winter period; main recommended uses are for general
interior
lighting and low-level external movement. They are cheap to buy but
are
relatively expensive to run.
n Tungsten halogen lamp Compact fitting with high light output, and
suitable
for all general area floodlighting. They are easy to mount, and
have a more
effective focused beam than the filament lamp. These lamps
generally have
a life of twice that of filament lamps, and quartz lamps have a
higher degree
of resistance to thermal shock than glass filament lamps. They are
dearer than
filament lamps and are still relatively expensive to run but should
be considered
if the running time is in the region of 1,500 hours annually.
n Mercury tungsten lamps Compact, efficient, with a good lamp life,
and do
not need the expensive starting gear of the vapour discharge lamps.
They can be
used for internal and external area lighting where lamps are not
mounted above
9.000 m high. These are high-cost lamps but are cheap to run.
n Mercury discharge lamps High-efficiency lamps with a long life;
can be
used for area lighting where lamps are mounted above 9.000 m high.
Costs for
lamps and control gear are high but the running costs are
low.
n Tubular fluorescent lamps Uniformly bright in all directions;
used when a
great concentration of light is not required; efficient, with a
range of colour
values. These lamps have a long life and are economical to
run.
n High-pressure sodium discharge lamps Compact, efficient, with a
long
life. For the best coverage without glare they should be mounted
above 13.500 m
high. Cost for lamp and control gear is high but running costs are
low, which
makes them suitable for area lighting.
Apart from the cost of the lamps and the running charges,
consideration must
be given to the cost of cables, controlling equipment, mounting
poles, masts
or towers. A single high tower may well give an overall saving
against using a
number of individual poles or masts in spite of the high initial
cost for the tower.
Consideration can also be given to using the scaffold, incomplete
structure or the
mast of a tower crane for lamp-mounting purposes, each subject to
earthing.
32 Advanced Construction Technology
nnn SITE LIGHTING INSTALLATIONS
When deciding upon the type and installation layout for
construction site lighting,
consideration must be given to the nature of the area and work to
be lit, and also to
the type or types of lamp to be used. These aspects can be
considered under the
following headings:
n beam floodlighting;
n walkway lighting;
n local lighting.
EXTERNAL AND LARGE CIRCULATION AREAS
These areas may be illuminated by using mounted lamps situated
around the
perimeter of the site or in the corners of the site; alternatively,
overhead
illumination using dispersive fittings can be used. The main
objectives of area
lighting are to enable staff and machinery to move around the site
in safety and to
give greater security to the site. Areas of local danger such as
excavations and
obstructions should, however, be marked separately with red warning
lights or
amber flashing lamps. Tungsten filament, mercury vapour or tungsten
halogen
lamps can be used, and these should be mounted on poles, masts or
towers
according to the lamp type and wattage. Typical mounting heights
for various
lamps and wattages are shown in Table 1.3.2.
Large areas are generally illuminated by using large, high-mounted
lamps,
whereas small areas and narrow sites use a greater number of
smaller fittings. By
mounting the lamps as high as practicable above the working level
glare is reduced,
and by lighting the site from at least two directions the formation
of dense shadows
is also reduced. The spacing of the lamps is also important if
under-lit and over-lit
areas are to be avoided. Figures 1.3.2 and 1.3.3 show typical lamps
and the
recommended spacing ratios.
Dispersive lighting is similar to an ordinary internal overhead
lighting
system, and is suitable for both exterior and interior area
lighting where overhead
Table 1.3.2 Mounting heights
Tungsten filament 200 4.500
Lighting building sites 35
suspension is possible. Ordinary industrial fittings should not be
used because of the
adverse conditions that normally prevail on construction sites. The
fittings selected
should therefore be protected against rust, corrosion and water
penetration. To
obtain a reasonable spread of light the lamps should be suspended
evenly over the
area to be illuminated, as shown diagrammatically in Fig. 1.3.4.
Tungsten filament,
mercury vapour and fluorescent trough fittings are suitable and
should be
suspended at a minimum height according to their type and wattage.
Typical
suspension heights are shown in Table 1.3.3.
Most manufacturers provide guidance as to the choice of lamps or
combination
of lamps, but a simple method of calculating lamp requirements is
as follows:
1. Decide upon the service illuminance required, and double this
figure to obtain
the target value.
3. Choose lamp type.
Number of lamps required =
4. Repeat stage 3 for different lamp types to obtain the most
practicable and
economic arrangement.
5. Consider possible arrangements, remembering that:
n larger lamps give more lumens per watt and are generally more
economic to run;
n fewer supports simplify wiring and aid overall economy;
n corner siting arrangements are possible;
n clusters of lamps are possible.
The calculations when using dispersive lighting are similar to
those given above for
mounted area lighting except for the formula in stage 2, which has
a utilisation
factor of 0.27 instead of 0.23.
BEAM FLOODLIGHTING
Tungsten filament or mercury vapour lamps can be used, but this
technique is
limited in application on construction sites to supplementing other
forms of
lighting. Beam floodlights are used to illuminate areas from a
great distance. The
total lumens required
0.23
Tungsten filament 200 2.500
36 Advanced Construction Technology
Lighting building sites 37
beam of light is intense, producing high glare, and it should
therefore be installed to
point downwards towards the working areas. Generally the lamps are
selected direct
from the manufacturer’s catalogue without calculations.
WALKWAY LIGHTING
Tungsten filament and fluorescent lamps can be used to illuminate
access routes
such as stairs, corridors and scaffolds. Bulkhead fittings that can
be safely installed
with adequate protection to the wiring can be run off a mains
voltage of 230 V
single-phase, but if they are in a position where they can be
handled a reduced
voltage of 110 V single-phase should be used. Festoon lighting, in
which the ready-
wired lampholders are moulded to the cable itself, can also be
used. A standard
festoon cable would be 100.000 m long with rainproof lampholders
and protective
shades or guards at 3.000 m or 5.000 m centres using 40 W or 60 W
tungsten
filament bulbs for the respective centres. See Fig. 1.3.5. For
lighting to scaffolds
of four- or five-board width 60 W lamps should be used, placed at
not more than
6.000 m centres and preferably at least 2.400 to 3.000 m above the
working platform
either to the wall side or centrally over the scaffold.
LOCAL LIGHTING
Clusters of pressed glass reflector floodlamps, tungsten filament
lamps, festoons
and adjustable fluorescents can be used to increase the surface
illumination at local
points, particularly where finishing trades are involved. These
fittings must be
portable so that shadow casting can be reduced or eliminated from
the working
plane: therefore it is imperative that these lights are operated
off a reduced voltage
of 110 V single-phase. Fluorescent tubes do not usually work at a
reduced voltage,
so special fittings working off a 110 V single-phase supply that
internally increase
the voltage are used. Typical examples of suitable lamps are shown
in Fig. 1.3.6.
As an alternative to a system of static site lighting connected to
the site mains,
electrical supply mobile lighting sets are available. These consist
of a diesel-
engine-driven generator and a telescopic tower with a cluster of
tungsten iodine
lamps. These are generally cheaper to run than lamps operating off
a mains supply.
Small two-stroke generator sets with a single lamp attachment
suitable for small,
isolated positions are also available.
Another system that can be used for local lighting is flame lamps,
which
normally use propane gas as the fuel. The ‘bulb’ consists of a
mantle, and a reflector
completes the lamp fitting, which is attached to the fuel bottle by
a flexible tube.
These lamps produce a great deal of local heat and water vapour;
the latter may
have the effect of slowing down the drying out of the building. An
alternative fuel
to propane gas is butane gas, but this fuel will not usually
vaporise at temperatures
below −1 °C.
Whichever method of illumination is used on a construction site it
is always
advisable to remember the axiom ‘A workman can only be safe and
work well when
he can see where he is going and what he is doing.’
38 Advanced Construction Technology
Lighting building sites 39
Figure 1.3.6 Local lighting: suitable lamps and fittings
Approximately one-fifth of the working force of the United Kingdom
is employed
either directly or indirectly by the building industry. Therefore
any fluctuation in
productivity will affect a large number of people. The general loss
in output in the
construction industry in normal circumstances during the winter
period is about
10%, which can result in the underemployment of staff, plant and
fixed assets
together with the loss of good trading relations with suppliers due
to goods ordered
not being called forward for delivery. A severe winter can treble
the typical loss
of output quoted above, resulting in loss of cash flow to the main
contractor and
subcontractors, plus reduced pay to employees. There will also be
lower profits,
or a profit loss for contractors, and many skilled operatives may
leave the industry
in search of more secure occupations. The building owner also
suffers by the delay
in completing the building, which could necessitate extending the
borrowing
period for the capital to finance the project or the loss of a
prospective tenant
or buyer.
The major factor in determining the progress of works on site
during the
winter period is the weather. Guidance as to the likely winter
weather conditions
for various areas of the United Kingdom can be obtained from maps,
charts and
statistical data issued by the Meteorological Office, and this is
useful for long-term
planning, whereas in the short term reliance is placed upon local
knowledge, daily
forecasts and the short-term monthly weather forecasts. The
uncertain nature
of the climate in the United Kingdom often discourages building
contractors from
investing in plant and equipment for winter-building techniques and
protective
measures that may prove to be unnecessary. Contractors must
therefore assess
the total cost of possible delays against the capital outlay
required for plant and
equipment to enable them to maintain full or near-full production
during the
winter period.
nnn EFFECTS OF WEATHER
Weather conditions that can have a delaying effect on building
activities are rain,
high winds, low temperatures, snow and poor daylight levels; the
worst effects
obviously occur when more than one of the above conditions occur
simultaneously.
Rain
Rain affects site access and movement, which in turn increases site
hazards,
particularly those associated with excavations and earth-moving
works. It also
causes discomfort to operatives, thus reducing their productivity
rate. Delays
with most external operations, such as bricklaying and concreting,
are usually
experienced, particularly during periods of heavy rainfall. Damage
can be caused to
unprotected materials stored on site and in many cases to newly
fixed materials or
finished surfaces. The higher moisture content of the atmosphere
will also delay the
drying out of buildings. If high winds and rain occur together,
rain penetration and
site hazards are considerably increased.
High winds
Apart from the discomfort felt by operatives, high winds can also
make activities such
as frame erection and the fixing of sheet cladding very hazardous.
They can also limit
the operations that can be carried out by certain items of plant
such as tower cranes
and suspended cradles. Positive and negative wind pressures can
also cause damage
to partially fixed claddings, incomplete structures and materials
stored on site.
Low temperatures
As the air temperature approaches freezing point many site
activities are slowed
down. These include excavating, bricklaying, concreting, plastering
and painting,
until they cease altogether at subzero temperatures; also,
mechanical plant can be
difficult to start, and stockpiles of materials can become frozen
and difficult to
move. General movement and circulation around the site becomes
hazardous,
creating with the low temperatures general discomfort and danger
for site
personnel. When high winds are experienced with low temperatures
they
will aggravate the above-mentioned effects.
Snow
This is one of the most variable factors in British weather,
ranging from an average
of five days a year on which snow falls on low ground in the
extreme south-west to
35 days in the north-east of Scotland. Snow will impair the
movement of labour,
plant and materials, as well as create uncomfortable working
conditions. Externally
stored materials will become covered with a layer of snow, making
identification
difficult in some cases. This blanket of snow will also add to
the
42 Advanced Construction Technology
load to be carried by all horizontal surfaces. High winds
encountered with falling
snow can cause drifting, which could increase the site hazards and
personal
discomfort, and decrease general movement around the site.
It should be appreciated that the adverse conditions described
above could have
an adverse effect on site productivity, even if they are not
present on the actual site,
by delaying the movement of materials to the site from suppliers
outside the
immediate vicinity.
nnn WINTER-BUILDING TECHNIQUES
The major aim of any winter-building method or technique is to
maintain an
acceptable rate of productivity. Inclement weather conditions can
have a very
quick reaction on the transportation aspect of site operations,
movement of vehicles
around the site and, indeed, off the site, which will be impaired
or even brought to a
complete standstill unless firm access roads or routes are
provided, maintained and
kept free of snow. These access roads should extend right up to the
discharge points
to avoid the need for unnecessary double handling of materials. If
the access roads
and hardstandings form part of the contract and are suitable, these
could be
constructed at an early stage in the contract before the winter
period. If the
permanent road system is not suitable in layout for contractual
purposes,
temporary roads of bulk timbers, timber or concrete sleepers,
compacted
hardcore or proprietary metal tracks could be laid.
Frozen ground can present problems with all excavating activities.
Most
excavating plant can operate in frozen ground up to a depth of 300
mm, but at
a reduced rate of output: this is particularly true